A solution commonly used to obtain coils from metallic rods is to use a laying head comprising a rotor in which a rod conveying and coil forming tube is fixed. The rotor is fixed in overhanging manner on a stator body by means of two bearings or supports and may thus turn about its axis. The stator body is in turn rigidly constrained to a base. The rotor turns about its axis generally at high angular speeds, which may exceed 2000 rpm. The rotation of the rotor is be generated by an external motor connected by means of a bevel gear transmission. Laying heads types, in which the rotors comprise the motor therein and coaxially fit the motor stator, are also known.
The rolled product, during the rotation of the laying head, is curved by the tube to form a succession of coils of defined diameter, which are arranged by falling on an evacuation conveyor belt to be cooled and conveyed to the collection and stacking pit.
An alternative solution for obtaining coils from metallic wire rods is to use solutions which provide the elimination of the coil conveying and forming tube. For example, document EP-A-779115 describes a laying head which instead of the coil forming tube uses a spiral shaped conveying groove obtained between two rotating bell-shaped members, an inner one and an outer one, which are mutually integral and fixed by means of a flange to the mandrel. The head is provided with four of more grooves which may be used alternatively for conveying and guiding the rolled product in the laying head.
The two bells are generally made of light materials, such as light alloys or composite materials, which make it possible to reach high rotation speeds. The grooves may be coated with wear-proof material to extend their working life.
In the known systems, two laying heads arranged side-by-side are normally provided, which can be selectively activated with the pass line of the rolled product by means of rails. A first laying head comprises a rotor in which a bell-shaped member is fixed, the bell-shaped member being provided on its outer surface with four or more grooves which can be alternatively used for conveying and guiding the wire rod in the laying head. A second laying head comprises a rotor in which a wire rod conveying and coil forming tube is fixed.
Disadvantageously, when the product type has to be changed, e.g. to pass from rod to wire rod or vice versa, the two laying heads must be moved along the rails, arranged transversally to the pass line of the rolled product, so as to move the first laying head away from said pass line and approach and align the second laying head to said pass line.
This solution, however, implies considerable dimensions of the system and long production change times.
The need is therefore felt to make an innovative laying head which makes it possible to overcome the aforesaid drawbacks.